From 1 to 21 August, 8 cases of Legionnaire’s disease were reported to the Regional Health Agency for the Paris Region; 5 of these victims resided at a care facility for the elderly in the city of Meudon and 2 others were living nearby. All eight, whose average age was 84, were hospitalised with 6 being placed in intensive care; 3 of them died.
The “level 1 suspicion of a group outbreak” procedure was activated. An investigation revealed that all victims happened to frequent a geographic zone within 2.5 km of the care facility.
A spot check conducted on 20 August found a level of contamination equal to 7,000,000 CFU/litre of Legionella pneumophila serogroup 1 stemming from a water cooling tower at an auto plant. The tower was shut down the day after receiving these results. Its circuits were then drained, cleaned and disinfected.
Some findings from the epidemiological and environmental investigations undertaken by the Health Monitoring Institute indicated that the most plausible (but perhaps not the only) source of contamination behind this group outbreak was the cooling tower. A number of arguments supported this hypothesis:
- the identity and rarity of the clinical and environmental strains, isolated at the suspected cooling tower. Given the existence of endemic strains, the similarity of clinical and environmental strains had not always been sufficient to establish a causal relationship. In this case however, causality was definitely prevalent by virtue of identifying the same isolated strain for the first time in epidemiologically-correlated clinical and environmental samples;
- matching climatological data (dominant wind directions, temperature, relative humidity);
- absence of urban obstacles to the spreading of aerosols released from a cooling tower in the same zone;
- results of environmental surveys conducted for the specific cases analysed, which failed to indicate any other source of contamination by Legionella pneumophila serogroup 1.
A biocide shock had been systematically performed 48 hours prior to the monthly environmental monitoring sample taken at the tower. This outbreak highlighted a potential absence in the environmental sampling when systematic preliminary disinfection was practised.
